Non-inductive film-type cylindrical resistor

ABSTRACT

A film of electrically resistive material is provided on an elongated ceramic cylinder, in such a manner that there is a gap in the resistive material along the full length of one side of the cylinder and parallel to the cylinder axis. The gap is sufficiently wide that the squeegee of a silk-screening apparatus may be disposed therebetween at one point in the silk-screening process which is employed to manufacture the resistor. There is thus no necessity for overprinting at any time during silkscreening, the result being that no smudged or voltage-breakdown regions are created. The resistive film pattern is non-inductive, and comprises a serpentine wave formed of hairpinshaped portions which are disposed closely adjacent each other.



1. A film-type electrical resistor, which comprises: a. an elongated cylindrical heat-resistant substrate, b. an electrically resistive film adherently provided by the silk-screen process on the exterior cylindrical surface of said substrate, said resistive film comprising an elongated narrow strip of resistive material, said strip having such a cross-sectional shape, in a direction perpendicular to the length of said strip, that the exterior surfaces of the edges of said strip converge toward said cylindrical surface in a feathered manner, said film being present on substantial portions of said surface, but being absent at a gaP which extends along the full length of one side of said surface parallel to the axis of said substrate, and c. termination means electrically connected to opposite end portions of said resistive film, and permitting connection of said film in an electrical circuit.
 2. The invention as claimed in claim 1, in which the width of said gap is at least 15 thousandths of an inch.
 3. The invention as claimed in claim 1, in which said strip is shaped in a serpentine manner, whereby current flows in opposite directions through adjacent portions of said strip, thereby minimizing the inductance of the resistor.
 4. The invention as claimed in claim 3, in which said serpentine strip comprises a multiplicity of hairpin-shaped portions the arms of which are substantially parallel to each other, said arms being connected to each other by base portions, and in which each of said arms is spaced less than 100 thousandths of an inch from each adjacent arm to thereby achieve effective cancellation of the inductance of the resistor.
 5. The invention as claimed in claim 4, in which the width of said strip is substantially equal to the widths of the spaces between adjacent arms of said hairpin-shaped portions.
 6. The invention as claimed in claim 4, in which the width of said strip is in the range of about 8 thousandths of an inch to about 100 thousandths of an inch, and in which the widths of the spaces between adjacent arms of said hairpin-shaped portions is in the range of about 8 thousandths of an inch to about 50 thousandths of an inch.
 7. The invention as claimed in claim 4, in which said arms of said hairpin-shaped portions extend circumferentially of said cylindrical surface, and in which said base portions extend generally longitudinally of said cylindrical surface, one row of said base portions being on one side of said gap, the other row of said base portions being on the opposite side of said gap, said rows extending parallel to the substrate axis along circumferentially-offset longitudinal side portions of said surface.
 8. The invention as claimed in claim 1, in which said cylindrical substrate is a solid ceramic cylinder, and is not hollow.
 9. The invention as claimed in claim 1, in which said termination means comprises highly conductive films adherently provided at opposite ends of said cylindrical surface and in electrical contact with opposite end portions of said resistive film, and further comprises conductive end caps press fit over said conductive films and connected to leads which extend outwardly from the resistor.
 10. The invention as claimed in claim 1, in which the maximum thickness of said film is in the range of about 0.0005 inch to about 0.002 inch.
 11. A low-inductance film-type resistor, which comprises: a. an elongated cylindrical substrate formed of a heat-resistant ceramic, said ceramic being solid, not hollow, for the full length thereof, the cylindrical surface of said substrate being smooth and ungrooved, b. a resistive film adherently provided by the silk-screen process directly onto the exterior cylindrical surface of said substrate, the thickness of said film being between about 0.0005 inch and about 0.002 inch, the exterior surfaces of the edges of said film tapering in feathered manner toward the exterior cylindrical surface of said substrate, said film being present on major portions of said surface, but being absent at all portions of a gap which extends along the full length of one side of said surface parallel to the axis of said substrate, the width of said gap being at least 15 thousandths of an inch, said film comprising an elongated narrow strip of resistive material, said strip being shaped in a serpentine manner and being formed of a multiplicity of parallel arms connected by base portions, each of said parallel arms being spaced less than 100 thousandths of an inch from each adjacent arm, c. termination films formed of conductive material and adherently provided on said cylindrical surface at opposite ends thereof, said films being respectively connected to opposite end portions of said serpentine strip, d. end caps press fit over said conductive films and being connected to leads, and e. means to encapsulate said film-coated substrate to environmentally protect the same.
 12. The invention as claimed in claim 11, in which said arms extend circumferentially of said cylindrical surface and said base portions extend generally longitudinally thereof, and in which said base portions are disposed on opposite sides of said gap.
 13. The invention as claimed in claim 11, in which the width of said strip is substantially equal to the spacing between adjacent arms.
 14. The invention as claimed in claim 11, in which the width of said strip is in the range of about 0.008 inch to about 0.100 inch, in which the width of each of the spaces between adjacent arms is in the the range of about 0.008 inch to about 0.050 inch.
 15. The invention as claimed in claim 1, in which said termination means comprises conductive end caps mounted over opposite ends of said substrate.
 16. The invention as claimed in claim 11, in which said film is in the form of an elongated narrow serpentine strip each arm of which is parallel to and less than 100 thousandths of an inch distant from each adjacent arm, whereby current flows in opposite directions through adjacent arms and because of the arm proximity creates an effective inductance-cancellation action. 